This invention relates to solid electrolyte capacitors which include safety fuzes, and more particularly to such a capacitor having an improved mechanical connection of its cathode body to a paddle of its leadframe.
Prior art constructions for providing solid electrolyte capacitors with safety fuzes have in common the need to provide support for the body of a capacitor having a fuze as the cathode electrical connection to a leadframe during encapsulation of the capacitor.
Shirn and Maher U.S. Pat. No. 4,107,762 teach supporting a capacitor body on a paddle of a leadframe by means of an intervening deposit of an insulating epoxy resin. However, the process for mounting the capacitor body on the epoxy entails pressing the body into epoxy, which results in varying thicknesses of insulation from one body to another, even on the same leadframe. In worst case mounting of a capacitor body on an epoxy layer, the uneven surface of the body protrudes through the epoxy so that the body contacts the paddle to short out any fuze interconnection between the paddle and the body.
Ideally, during manufacturing, the capacitor body should be held securely in place, because device handling prior to encapsulation, and encapsulation itself, apply mechanical forces and stress to the device. Such stress is the cause of broken joints between the cathode body and the capacitor mounting, and also broken and weakened connections between the capacitor body/fuze/cathode lead assembly. This type of defect or separation is very difficult to detect in the finished capacitor if it has gone undetected prior to encapsulation. The result could be a point contact within the device itself and the failure mode could show up at any time in the future as an open.
All prior art mountings for fuzed capacitors provide little mechanical support at the cathode end of the device. This can have a negative impact on the yield and subsequent reliability of the capacitor.
An object of this invention is to provide an easily manufacturable technique that provides high mechanical strength to the cathode end of a fuzed capacitor. It is another object of this invention to provide uniform and continuous insulation between a capacitor body and a paddle on a leadframe. Another object is to provide that desired uniform and continuous insulation by a simplified procedure that eliminates need for complex pressure control in the mounting of the body on the paddle.